1 // Copyright 2013 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // This file implements various field and method lookup functions.
14 // Internal use of LookupFieldOrMethod: If the obj result is a method
15 // associated with a concrete (non-interface) type, the method's signature
16 // may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
19 // LookupFieldOrMethod looks up a field or method with given package and name
20 // in T and returns the corresponding *Var or *Func, an index sequence, and a
21 // bool indicating if there were any pointer indirections on the path to the
22 // field or method. If addressable is set, T is the type of an addressable
23 // variable (only matters for method lookups).
25 // The last index entry is the field or method index in the (possibly embedded)
26 // type where the entry was found, either:
28 // 1) the list of declared methods of a named type; or
29 // 2) the list of all methods (method set) of an interface type; or
30 // 3) the list of fields of a struct type.
32 // The earlier index entries are the indices of the embedded struct fields
33 // traversed to get to the found entry, starting at depth 0.
35 // If no entry is found, a nil object is returned. In this case, the returned
36 // index and indirect values have the following meaning:
38 // - If index != nil, the index sequence points to an ambiguous entry
39 // (the same name appeared more than once at the same embedding level).
41 // - If indirect is set, a method with a pointer receiver type was found
42 // but there was no pointer on the path from the actual receiver type to
43 // the method's formal receiver base type, nor was the receiver addressable.
45 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
46 // Methods cannot be associated to a named pointer type
47 // (spec: "The type denoted by T is called the receiver base type;
48 // it must not be a pointer or interface type and it must be declared
49 // in the same package as the method.").
50 // Thus, if we have a named pointer type, proceed with the underlying
51 // pointer type but discard the result if it is a method since we would
52 // not have found it for T (see also issue 8590).
53 if t := asNamed(T); t != nil {
54 if p, _ := safeUnderlying(t).(*Pointer); p != nil {
55 obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
56 if _, ok := obj.(*Func); ok {
57 return nil, nil, false
63 return lookupFieldOrMethod(T, addressable, pkg, name)
66 // TODO(gri) The named type consolidation and seen maps below must be
67 // indexed by unique keys for a given type. Verify that named
68 // types always have only one representation (even when imported
69 // indirectly via different packages.)
71 // lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
72 func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
73 // WARNING: The code in this function is extremely subtle - do not modify casually!
76 return // blank fields/methods are never found
79 typ, isPtr := deref(T)
81 // *typ where typ is an interface or type parameter has no methods.
83 // don't look at under(typ) here - was bug (issue #47747)
84 if _, ok := typ.(*TypeParam); ok {
87 if _, ok := under(typ).(*Interface); ok {
92 // Start with typ as single entry at shallowest depth.
93 current := []embeddedType{{typ, nil, isPtr, false}}
95 // Named types that we have seen already, allocated lazily.
96 // Used to avoid endless searches in case of recursive types.
97 // Since only Named types can be used for recursive types, we
98 // only need to track those.
99 // (If we ever allow type aliases to construct recursive types,
100 // we must use type identity rather than pointer equality for
101 // the map key comparison, as we do in consolidateMultiples.)
102 var seen map[*Named]bool
104 // search current depth
105 for len(current) > 0 {
106 var next []embeddedType // embedded types found at current depth
108 // look for (pkg, name) in all types at current depth
109 var tpar *TypeParam // set if obj receiver is a type parameter
110 for _, e := range current {
113 // If we have a named type, we may have associated methods.
114 // Look for those first.
115 if named := asNamed(typ); named != nil {
117 // We have seen this type before, at a more shallow depth
118 // (note that multiples of this type at the current depth
119 // were consolidated before). The type at that depth shadows
120 // this same type at the current depth, so we can ignore
125 seen = make(map[*Named]bool)
129 // look for a matching attached method
130 if i, m := lookupMethod(named.methods, pkg, name); m != nil {
132 // caution: method may not have a proper signature yet
133 index = concat(e.index, i)
134 if obj != nil || e.multiples {
135 return nil, index, false // collision
138 indirect = e.indirect
139 continue // we can't have a matching field or interface method
142 // continue with underlying type
147 switch t := typ.(type) {
149 // look for a matching field and collect embedded types
150 for i, f := range t.fields {
151 if f.sameId(pkg, name) {
153 index = concat(e.index, i)
154 if obj != nil || e.multiples {
155 return nil, index, false // collision
158 indirect = e.indirect
159 continue // we can't have a matching interface method
161 // Collect embedded struct fields for searching the next
162 // lower depth, but only if we have not seen a match yet
163 // (if we have a match it is either the desired field or
164 // we have a name collision on the same depth; in either
165 // case we don't need to look further).
166 // Embedded fields are always of the form T or *T where
167 // T is a type name. If e.typ appeared multiple times at
168 // this depth, f.typ appears multiple times at the next
170 if obj == nil && f.embedded {
171 typ, isPtr := deref(f.typ)
172 // TODO(gri) optimization: ignore types that can't
173 // have fields or methods (only Named, Struct, and
174 // Interface types need to be considered).
175 next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
180 // look for a matching method
181 if i, m := t.typeSet().LookupMethod(pkg, name); m != nil {
183 index = concat(e.index, i)
184 if obj != nil || e.multiples {
185 return nil, index, false // collision
188 indirect = e.indirect
192 if i, m := t.iface().typeSet().LookupMethod(pkg, name); m != nil {
194 index = concat(e.index, i)
195 if obj != nil || e.multiples {
196 return nil, index, false // collision
200 indirect = e.indirect
206 // found a potential match
207 // spec: "A method call x.m() is valid if the method set of (the type of) x
208 // contains m and the argument list can be assigned to the parameter
209 // list of m. If x is addressable and &x's method set contains m, x.m()
210 // is shorthand for (&x).m()".
211 if f, _ := obj.(*Func); f != nil {
212 // determine if method has a pointer receiver
213 hasPtrRecv := tpar == nil && f.hasPtrRecv()
214 if hasPtrRecv && !indirect && !addressable {
215 return nil, nil, true // pointer/addressable receiver required
221 current = consolidateMultiples(next)
224 return nil, nil, false // not found
227 // embeddedType represents an embedded type
228 type embeddedType struct {
230 index []int // embedded field indices, starting with index at depth 0
231 indirect bool // if set, there was a pointer indirection on the path to this field
232 multiples bool // if set, typ appears multiple times at this depth
235 // consolidateMultiples collects multiple list entries with the same type
236 // into a single entry marked as containing multiples. The result is the
237 // consolidated list.
238 func consolidateMultiples(list []embeddedType) []embeddedType {
240 return list // at most one entry - nothing to do
243 n := 0 // number of entries w/ unique type
244 prev := make(map[Type]int) // index at which type was previously seen
245 for _, e := range list {
246 if i, found := lookupType(prev, e.typ); found {
247 list[i].multiples = true
258 func lookupType(m map[Type]int, typ Type) (int, bool) {
259 // fast path: maybe the types are equal
260 if i, found := m[typ]; found {
264 for t, i := range m {
265 if Identical(t, typ) {
273 // MissingMethod returns (nil, false) if V implements T, otherwise it
274 // returns a missing method required by T and whether it is missing or
275 // just has the wrong type.
277 // For non-interface types V, or if static is set, V implements T if all
278 // methods of T are present in V. Otherwise (V is an interface and static
279 // is not set), MissingMethod only checks that methods of T which are also
280 // present in V have matching types (e.g., for a type assertion x.(T) where
281 // x is of interface type V).
283 func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
284 m, typ := (*Checker)(nil).missingMethod(V, T, static)
288 // missingMethod is like MissingMethod but accepts a *Checker as
289 // receiver and an addressable flag.
290 // The receiver may be nil if missingMethod is invoked through
291 // an exported API call (such as MissingMethod), i.e., when all
292 // methods have been type-checked.
293 // If the type has the correctly named method, but with the wrong
294 // signature, the existing method is returned as well.
295 // To improve error messages, also report the wrong signature
296 // when the method exists on *V instead of V.
297 func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method, wrongType *Func) {
298 // fast path for common case
303 if ityp, _ := under(V).(*Interface); ityp != nil {
304 // TODO(gri) the methods are sorted - could do this more efficiently
305 for _, m := range T.typeSet().methods {
306 _, f := ityp.typeSet().LookupMethod(m.pkg, m.name)
315 // both methods must have the same number of type parameters
316 ftyp := f.typ.(*Signature)
317 mtyp := m.typ.(*Signature)
318 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
321 if ftyp.TypeParams().Len() > 0 {
322 panic("method with type parameters")
325 // If the methods have type parameters we don't care whether they
326 // are the same or not, as long as they match up. Use unification
327 // to see if they can be made to match.
328 // TODO(gri) is this always correct? what about type bounds?
329 // (Alternative is to rename/subst type parameters and compare.)
330 u := newUnifier(true)
331 u.x.init(ftyp.TypeParams().list())
332 if !u.unify(ftyp, mtyp) {
340 // A concrete type implements T if it implements all methods of T.
341 for _, m := range T.typeSet().methods {
342 // TODO(gri) should this be calling lookupFieldOrMethod instead (and why not)?
343 obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
345 // Check if *V implements this method of T.
348 obj, _, _ = lookupFieldOrMethod(ptr, false, m.pkg, m.name)
350 return m, obj.(*Func)
354 // we must have a method (not a field of matching function type)
360 // methods may not have a fully set up signature yet
362 check.objDecl(f, nil)
365 // both methods must have the same number of type parameters
366 ftyp := f.typ.(*Signature)
367 mtyp := m.typ.(*Signature)
368 if ftyp.TypeParams().Len() != mtyp.TypeParams().Len() {
371 if ftyp.TypeParams().Len() > 0 {
372 panic("method with type parameters")
375 // If the methods have type parameters we don't care whether they
376 // are the same or not, as long as they match up. Use unification
377 // to see if they can be made to match.
378 // TODO(gri) is this always correct? what about type bounds?
379 // (Alternative is to rename/subst type parameters and compare.)
380 u := newUnifier(true)
381 u.x.init(ftyp.RecvTypeParams().list())
382 if !u.unify(ftyp, mtyp) {
390 // missingMethodReason returns a string giving the detailed reason for a missing method m,
391 // where m is missing from V, but required by T. It puts the reason in parentheses,
392 // and may include more have/want info after that. If non-nil, wrongType is a relevant
393 // method that matches in some way. It may have the correct name, but wrong type, or
394 // it may have a pointer receiver.
395 func (check *Checker) missingMethodReason(V, T Type, m, wrongType *Func) string {
398 if compilerErrorMessages {
399 mname = m.Name() + " method"
401 mname = "method " + m.Name()
403 if wrongType != nil {
404 if Identical(m.typ, wrongType.typ) {
405 if m.Name() == wrongType.Name() {
406 r = fmt.Sprintf("(%s has pointer receiver)", mname)
408 r = fmt.Sprintf("(missing %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
409 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
412 if compilerErrorMessages {
413 r = fmt.Sprintf("(wrong type for %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
414 mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
416 r = fmt.Sprintf("(wrong type for %s: have %s, want %s)",
417 mname, wrongType.typ, m.typ)
420 // This is a hack to print the function type without the leading
421 // 'func' keyword in the have/want printouts. We could change to have
422 // an extra formatting option for types2.Type that doesn't print out
424 r = strings.Replace(r, "^^func", "", -1)
425 } else if IsInterface(T) {
426 if isInterfacePtr(V) {
427 r = fmt.Sprintf("(%s is pointer to interface, not interface)", V)
429 } else if isInterfacePtr(T) {
430 r = fmt.Sprintf("(%s is pointer to interface, not interface)", T)
433 r = fmt.Sprintf("(missing %s)", mname)
438 func isInterfacePtr(T Type) bool {
439 p, _ := under(T).(*Pointer)
440 return p != nil && IsInterface(p.base)
443 // assertableTo reports whether a value of type V can be asserted to have type T.
444 // It returns (nil, false) as affirmative answer. Otherwise it returns a missing
445 // method required by V and whether it is missing or just has the wrong type.
446 // The receiver may be nil if assertableTo is invoked through an exported API call
447 // (such as AssertableTo), i.e., when all methods have been type-checked.
448 // If the global constant forceStrict is set, assertions that are known to fail
449 // are not permitted.
450 func (check *Checker) assertableTo(V *Interface, T Type) (method, wrongType *Func) {
451 // no static check is required if T is an interface
452 // spec: "If T is an interface type, x.(T) asserts that the
453 // dynamic type of x implements the interface T."
454 if IsInterface(T) && !forceStrict {
457 return check.missingMethod(T, V, false)
460 // deref dereferences typ if it is a *Pointer and returns its base and true.
461 // Otherwise it returns (typ, false).
462 func deref(typ Type) (Type, bool) {
463 if p, _ := typ.(*Pointer); p != nil {
469 // derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
470 // (named or unnamed) struct and returns its base. Otherwise it returns typ.
471 func derefStructPtr(typ Type) Type {
472 if p, _ := under(typ).(*Pointer); p != nil {
473 if _, ok := under(p.base).(*Struct); ok {
480 // concat returns the result of concatenating list and i.
481 // The result does not share its underlying array with list.
482 func concat(list []int, i int) []int {
484 t = append(t, list...)
488 // fieldIndex returns the index for the field with matching package and name, or a value < 0.
489 func fieldIndex(fields []*Var, pkg *Package, name string) int {
491 for i, f := range fields {
492 if f.sameId(pkg, name) {
500 // lookupMethod returns the index of and method with matching package and name, or (-1, nil).
501 func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
503 for i, m := range methods {
504 if m.sameId(pkg, name) {